1. Field of the Invention
The present invention relates to a method for adjusting focus bias in an optical disk device, in which a focus bias offset value at which the substantially-smallest jitter value of a high frequency signal is detected is set as an optimal focus bias offset value when a focus bias adjustment operation for an optical disk such as a DVD-RAM (Digital Versatile Disk Random Access Memory) is performed.
2. Description of the Related Art
An optical disk such as a DVD-ROM capable of reproducing lengthy high-quality video data and high-quality audio data, and an optical disk device such as a DVD player capable of reproducing video and audio data recorded on the DVD ROM have been commercialized and come into wide use.
In addition, recently, a rewritable optical disk such as a DVD-RAM and an optical disk device such as a DVD recorder capable of recording video and audio data on the DVD-RAM have been developed and are expected to be commercialized.
When a DVD-RAM is loaded into the optical disk device such as the DVD recorder, the device moves an optical pickup to a lead-in area, a preset initial position, and then performs an initial focusing servo operation. To perform the initial focusing servo operation, the optical disk device detects a just focus point with reference to a focusing error signal outputted from the optical pickup while vertically moving an objective lens in the optical pickup toward and away from the disk.
After completing such an initial focusing servo operation, the optical disk device moves the pickup to a data area to perform a focus bias adjustment operation for a focusing servo operation in the data area.
The focus bias adjustment operation is performed in such a manner that while a focus bias offset value, varying in a stepwise manner, is applied to an actuator provided in the optical pickup, a jitter value of a high frequency signal is detected, and a focus bias offset value at which the smallest jitter value is detected is set as an optimal focus bias offset value. Such a focus bias adjustment operation makes it possible to perform a focusing servo operation optimal for characteristics of the optical pickup or physical characteristics of the DVD-RAM.
However, a physical information data (PID) area having record patterns in an embossed form is recorded, in a dispersed manner, in the data area of an optical disk such as a general DVD-RAM. Thus, when the focus bias adjustment operation is performed, the high frequency signal is detected in a distorted abnormal form in the physical information data area. This causes an error in the jitter value measurement, thus incorrectly setting an optimal focus bias offset value. This results in an error in the focusing servo operation.